1. Field of the Invention
The present invention generally relates to the field of data communication networks, and more specifically, to using an information element including a hybrid acknowledgment map format to indicate receipt of data.
2. Description of the Background Art
Because information transmitted across a data communication network is subject to transmission errors such as data corruption or data loss, error control and/or correction is an integral part of existing data communication networks. Error control and/or correction allows devices using the data communication network to detect, and possibly correct, errors in the transmitted data. Existing data networks use many different methods for error control or error correction.
FIG. 1 is a block diagram representing a typical wireless data communication network 100. A base station 110 and multiple mobile stations 120 communicate data with each other using a communication protocol such as one compliant with the IEEE 802.16 standard. The data communication network 100 uses an Automatic Repeat Request (ARQ) scheme to detect correctly received data and retransmit data erroneously received or lost during transmission. ARQ schemes are commonly used because retransmission of data encountering transmission errors increases the reliability of communication between the mobile stations 120 and the base station 110. In an ARQ scheme, the receiving device automatically requests that the transmitting device retransmit received messages containing errors. Receiving a retransmission request causes the transmitting device to retransmit the requested message. When the message is correctly received, the receiving device transmits an acknowledgement (ACK) message. The requested message can be retransmitted until it is correctly received or the error persists beyond a specified number of retransmissions or persists beyond a specified time interval.
Conventional ARQ schemes use acknowledgment maps (ACK maps) to indicate correct or incorrect receipt of data sequences. By examining the ACK map, the transmitting device identifies the correctly received and incorrectly received segments of the transmitted data. ACK maps have different formats depending on the distribution of errors in the transmitted data. Currently, ACK maps are formatted as a bitmap or a block sequence listing.
When a bitmap is used, the ACK map contains information indicating correct or incorrect receipt of individual data segments. Thus, the bitmap format allows the ACK map to identify specific parts of the data incorrectly received and in need of retransmission. This allows for retransmission of the incorrectly received data segments rather than retransmission of all data.
When a block sequence listing is used, the ACK map contains information indicating whether or not a continuous block of data has been correctly or incorrectly received. However, the block sequence listing cannot indicate specific segments of the data which were correctly or incorrectly received. Thus, when the received data alternates between correct receipt and incorrect receipt, the block sequence listing cannot be used.
In existing ARQ schemes, information elements (IEs) are used to transmit multiple ACK maps. FIG. 2 shows an example of the fields within a typical information element (IE) 200. The IE 200 can be any formatted block of information, such as an ARQ feedback element compliant with the IEEE 802.16 standard.
The IE 200 includes a header 210 and a payload 220. The header 210 includes fields 212, 214 that specify characteristics of the payload 220 or the processing of the payload 220. In conventional ARQ schemes, the header includes a type field 212 and a quantity field 214. The type field 212 identifies the type of the ACK maps contained in the payload 220, and commonly comprises two bits. The quantity field 214 indicates how many ACK maps are contained in the payload 220. The payload 220 contains one to four ACK maps.
Because the type field 212 indicates the format of ACK maps in the payload 220, all ACK maps in an IE 200 must have the same format. Thus, when both bitmap formatted and sequence listing formatted ACK maps are necessary to describe data, multiple IEs 200 must be transmitted, with each IE 200 containing a different ACK map format. So, one IE 200 is necessary to transmit bitmap formatted ACK maps to identify data with correctly received and incorrectly received segments, and a second IE 200 is necessary to transmit sequence listing formatted ACK maps to identify continuous blocks of correctly received or incorrectly received data.
Because each IE 200 contains a header 210, as well as the ACK maps in the payload 220, transmitting additional IEs 200 increases the overhead necessary for ARQ schemes, reducing the bandwidth available for data transmission. As ACK maps are frequently transmitted, the overhead resulting from IE 200 transmission can significantly impair network performance.
Further, conventional IEs 200 and ACK maps have a limited size, which limits the amount of ACK maps that can be included in an IE 200. Typical ARQ schemes permit a maximum of four ACK maps to be included in an IE 200. Thus, incorrect determination of the ACK map format can further increase network usage by increasing the number of IEs 200 transmitted. Additionally, the limited ACK map size can require transmission of additional ACK maps and IEs 200 when the data contains multiple data segment sizes with different types of error distributions.
Therefore, there is a need for an acknowledgement map format capable of representing acknowledgment data in different formats that allows a single information element to include differently formatted acknowledgment maps.